Friday, April 22, 2016

Tonight's Sky for April 22: Full Apogee Moon

Tonight,
the Moon
will reach its full phase, which means that, as seen from Earth, it
is directly opposite the Sun in the sky as seen from Earth and is at
the half way point in its current orbit.

As
for lunar mechanics, the Moon is always half lit. The reason we don't
always see it as such is thanks to orientation in relation to us.
Right now, when the Moon is
opposite the Sun and on the far side of Earth, we can see all of its
lit side, which is why it appears to be “full.” In the coming
nights, we will start to see less of the Moon as its lit side starts
to turn away from us as seen from Earth and heads toward Third
Quarter.

In
addition, this will be, in terms of angular size, the smallest Full
Moon of the year. Why? The Moon is at apogee, a point in its orbit
that is farthest from Earth.

What
many people may not realize is the fact that the Moon (and all other
celestial bodies) do not orbit their parent bodies in circles, but
ellipses, which are slightly elongated circles. Result: any given day
of an orbital period, any orbiting body will be at a slightly
different distance from its parent body. As for the Moon, this
variance in orbit amounts to about 20,000 miles.

As for
tonight, the Moon will be about as far from Earth as it is going to
get. When it comes to practical implications, the difference will be
hard to notice with the naked eye to all but an experienced observer
but, in a telescope,
the difference will be obvious